Gas turbine engines used in aircraft include exhaust nozzles to eject gas and achieve thrust. Increased efficiency is achieved with variable area convergent/divergent nozzles. This is especially true where the engine also uses afterburning.
Each nozzle is formed of a plurality of circumferentially located adjustable sections. Each section includes a four-bar linkage with an A-frame supporting a pivot point. A convergent section is pivotally secured to the A-frame. A divergent flap is secured to the convergent flap and an external flap connected to the divergent flap. Each of these connections are made at two transversely spaced locations. There also is a mode strut connecting the divergent flap and including some lost motion travel.
Conventionally the A-frame is secured to the structural support and a mode strut bracket is also secured to the structural support. The external flap and the mode strut are secured to this mode strut bracket.
In this structure a plurality of tolerances are encountered. The sum of tolerances is accumulated from the structure to the A-frame, the A-frame to the convergent flap, the convergent flap to the divergent flap, the divergent flap to the external flap, the external flap to the mode strut bracket, and the mode strut bracket to the structural support. Since the tolerance deviation at one of the transversely spaced connections may be different from that at the other location, the accumulation of tolerances can end up with the external flap being angularly displaced. This can theoretically be an amount which would prevent installation of this flap. Even where the tolerances are not so extreme, it could require forcing of the connection. Any misalignment increases the wear during operation of the gas turbine nozzle.